Bug 870171 - Part 15: Add attemptPruneByDuration.
Bug 870171 - Part 16: Add attemptPruneBySize.
Bug 870171 - Part 17: Add pruneEvents and tests.
Bug 870171 - Part 18: Add pruneEnvironments and tests.
Bug 870171 - Part 19: Add attemptVacuum.
Bug 870171 - Part 20: Have BroadcastService start PruneService alarm.
Bug 870171 - Followup: Put deletion inside transactions, add final keyword.